CONTENTS

Genepn converts the input wave into a simulated neural activity
pattern (NAP) and summarises the NAP as a sequence of excitation
patterns (EPNs). The operation takes place in three stages: spectral
analysis, neural encoding, and temporal integration (Patterson et
al. 1995) . In the spectral analysis stage, the input wave is
converted into an array of filtered waves, one for each channel of the
auditory filterbank. The surface of the array of filtered waves is
AIMs representation of basilar membrane motion (BMM) as a function of
time (see genbmm). In the neural encoding stage, compression,
adaptation and, optionally, suppression, are used to convert each wave
from the filterbank into a simulation of the aggregate neural response
to that wave. The array of responses is AIMs simulation of the
multi-channel neural activity pattern (NAP) in the auditory nerve at
about the level of the cochlear nucleus (see gennap). Finally, the NAP
is converted into a sequence of excitation patterns (EPNs) by
calculating the envelope of the NAP and extracting spectral slices
from the envelope every frstep_epn ms (Patterson, 1994a). The
envelope is calculated continuously, by lowpass filtering the
individual channels of the NAP as they flow from the cochlea
simulation.

The excitation pattern produced by genepn is intended to simulate the
spectral representation of a sound as it occurs in the peripheral
auditory system after neural transduction at about the level of the
cochlea nucleus. As a result, the frequency resolution of the
analysis varies with the center frequency of the channel, and the
distribution of channels across frequency is chosen to match that in
the auditory system (Patterson and Moore, 1986; Glasberg and Moore,
1990). For details, see the manual entry for genbmm and Patterson
(1994a) The excitaion pattern is a plot of the activity in each
channel as a function of the centre frequency of the auditory filter
that defines the channel. In AIM, the suffix epn is used to
distinguish this spectral representation from the other spectral
representations provided by the software (asa auditory spectral
analysis, sgm auditory spectrogram, and cgm cochleogram).

The neural activity pattern produced by genepn is the same as that
produced by gennap. The primary differences are in the defaults for
the Displays and the fact that the Leaky Integration is used to
construct spectral slices from the NAP rather than simulating loss of
phase locking. As a result, this manual entry is restricted to
describing the options that differ from those in gennap.

The default values for three of the display options are reset to
produce a spectral format rather than a landscape. Specifically,
display=excitation, bottom=0 and top=2500. The number of channels is
increased to 128 to ensure reasonable frequency resolution in the
excitation pattern display.

NOTE: The cochlea simulations impose compression of one form or
another on the NAP and the notes on compression in the man pages for
gennap apply to genepn as well.

Permission to use, copy, modify, and distribute this software without fee
is hereby granted for research purposes, provided that this copyright
notice appears in all copies and in all supporting documentation, and that
the software is not redistributed for any fee (except for a nominal
shipping charge). Anyone wanting to incorporate all or part of this
software in a commercial product must obtain a license from the Medical
Research Council.

The MRC makes no representations about the suitability of this
software for any purpose. It is provided "as is" without express or
implied warranty.

THE MRC DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE, INCLUDING
ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS, IN NO EVENT SHALL
THE A.P.U. BE LIABLE FOR ANY SPECIAL, INDIRECT OR CONSEQUENTIAL DAMAGES
OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS,
WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION,
ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS
SOFTWARE.

The AIM software was developed for Unix workstations by John
Holdsworth and Mike Allerhand of the MRC APU, under the direction of
Roy Patterson. The physiological version of AIM was developed by
Christian Giguere. The options handler is by Paul Manson. The revised
SAI module is by Jay Datta. Michael Akeroyd extended the postscript
facilites and developed the xreview routine for auditory image
cartoons.

The project was supported by the MRC and grants from the U.K. Defense
Research Agency, Farnborough (Research Contract 2239); the EEC Esprit
BR Porgramme, Project ACTS (3207); and the U.K. Hearing Research Trust.

SunOS 5.6

GENEPN (1)

4 September 1995

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